The present invention relates to a method of producing plural device chips from a thin plate of a pyroelectric material.
In the past, a pyroelectric infrared detector for detecting infrared radiation emanating from an object has been used as a motion sensor for detecting the motion of a person. This infrared detector is mainly composed of a substrate of a material having pyroelectric effects such as a ceramic material, e.g., PbTiO3 or PZT, a single-crystal material, e.g., LiTaO3, and a high-molecular compound, e.g., PVF2, and a plurality of electrodes formed by depositing an infrared absorption material such as NiCr on opposite surfaces of the substrate.
As a production method for this kind of infrared detector, for example, Japanese Patent Early Publication [KOKAI] No. 10-2793 discloses a method of producing several hundreds of infrared detectors from a single wafer, which comprises the steps of forming circuit patterns of the pyroelectric infrared detectors on the wafer of a pyroelectric material having a thickness of 40 xcexcm and a diameter of 3 inches by use of a metal mask for photolithography, forming electrodes at required positions on the basis of the circuit patterns by depositing an infrared absorption material, and then performing a sandblast treatment or a dry-etching process to remove required regions of the wafer. The sandblast treatment is a manufacturing technique of cutting a workpiece or forming slots in the workpiece by blowing fine hard particles on the workpiece at a constant pressure. The dry-etching process comprises ion milling and RIE, which are used in the conventional semiconductor process.
The sandblast treatment has advantages that the treatment speed is high, and there is no need to use an expensive apparatus such as ion milling. On the contrary, when blowing the hard particles of inorganic materials on the wafer substrate, the polarization state of the pyroelectric material may be broken by static electricity developed on the substrate surface. As a result, there is a problem that variations in performance of the produced pyroelectric infrared devices occur, and as the worst desired device performance is not obtained. Moreover, in the case of producing large amounts of devices from a single thin wafer, there is another problem that much effort is needed to collect and arrange these devices.
In view of the above problems, an object of the present invention is to provide an improved method of producing plural device chips from a thin plate of a pyroelectric material.
That is, the method of the present invention comprises the following steps. First, a device substrate to be treated with a blast of hard particles is formed. The device substrate comprises the thin plate of the pyroelectric material, plural device-forming regions each having an electrode, which are defined on opposite two surfaces of the thin plate, and a circuit pattern formed on each of the opposite two surfaces to electrically connect the electrodes. Each of the device-forming regions is isolated from an adjacent device-forming region by a stock-removal portion. Then, an electrical connection is made between the circuit patterns formed on the opposite two surfaces of the device substrate to obtain a 3-dimensional circuit pattern, and the 3-dimensional circuit pattern is grounded so that all of the device-forming regions on the device substrate are at the same potential. Next, the device substrate having the 3-dimensional circuit pattern is treated with the blast to remove the pyroelectric material of the stock-removal portion, while leaving a bridge portion extending between adjacent device-forming regions and having the circuit patterns thereon, to thereby obtain a device-chip aggregate, in which adjacent device chips are coupled through the bridge portion. Subsequently, the device chips is separated from the device-chip aggregate by removing the bridge portion.
In the present invention, since all of the device-forming regions on the device substrate are maintained to be at the same potential by the presence of the circuit patterns on the bridge portions during the blast treatment, the polarization state of the pyroelectric material is not broken by static electricity. In addition, since plural device chips are provided as a device-chip aggregate by the blast treatment, the handling of the device-chip aggregate becomes easy, and it is possible to collect the device chips separated from the device-chip aggregate by removing the bridge portions, while maintaining an arrangement of the device chips.
In the above method, it is preferred that the electrodes and the circuit patterns are simultaneously formed by means of physical vapor deposition (PVD). In this case, it is possible to efficiently produce the device substrate.
In addition, it is preferred that the pyroelectric material of the stock-removal portion is removed such that the bridge portion is of a constricted shape having a small cross section in the middle between adjacent device chips. In this case, when separating the device chip from said device-chip aggregate, it is possible to break only the bridge portion without causing the propagation of cracks into the device chip.
In addition, it is preferred that the step of removing the bridge portion is performed by use of a table having holding means for holding the device-chip aggregate. In particular, it is preferred that the holding means has the capability of magnetically holding the device-chip aggregate on the table by use of a magnetic mask having an opening, and the step of removing the bridge portion is performed through the opening. In this case, it is possible to easily hold the device-chip aggregate on the table without contamination of the device-chip aggregate with adhesives for holding. In addition, since the bridge portion is removed through the opening formed in the magnetic mask, there is no need to worry about the contamination of the device chips with scattered particles generated when the bridge portion is removed by use of a laser.
In addition, it is preferred that one of the table and the magnetic mask has a projection on its surface, which can fit into a space between adjacent device chips of the device-chip aggregate. The positioning of the device-chip aggregate becomes easier, and it is possible to prevent the occurrence of a positional displacement of the device-chip aggregate during the removing step.
Moreover, it is preferred that the above method comprises the steps of, after the step of removing the bridge portion, catching the magnetic mask and separated device chips by use of a suction apparatus, which comprises a first suction means for catching the magnetic mask, second suction means for catching a required number of the device chips separated from the device-chip aggregate through first openings formed in the magnetic mask, and a third suction means for catching the rest of the device chips separated through second openings formed in the magnetic mask, transferring the magnetic mask and the device chips caught by the first, second and third suction means to a first position, releasing only the device chips caught by the second suction means at the first position, transferring the magnetic mask and the device chips caught by the first and third suction means to a second position, and releasing the device chips caught by the third suction means at the second position. In this case, it is possible to readily obtain an arrangement of the required number of device chips, which has an increased distance between adjacent device chips, from an original arrangement of the device chips of the device-chip aggregate. Therefore, it is effective to improve the efficiency of collecting and arranging the device chips.
It is preferred that the step of making the electrical connection between the circuit patterns comprises the steps of forming a connection end of one of the circuit patterns on a surface having a connection end of the other circuit pattern, placing a metal foil between the connection ends, and securing the metal foil by forming a resist film on the device substrate. In addition, the step of making the electrical connection between the circuit patterns may comprise the steps of forming a connection end of one of the circuit patterns on a surface having the connection end of the other circuit pattern, placing a metal foil having magnetism between the connection ends, and securing the metal foil by magnetic force. Moreover, the step of making the electrical connection between the circuit patterns may comprise the steps of forming a through hole in the thin plate of the pyroelectric material by use of a laser, and coating an interior surface of the through hole with an electrically conductive material. According to these methods, it is possible to readily make the electrical connection between the circuit patterns with reliability.
A further object of the present invention is to provide a method of producing device chips from a thin plate of a pyroelectric material, which comprises the following steps. That is, in this method, a device substrate to be treated with a blast of hard particles is firstly formed. The device substrate comprises the thin plate of the pyroelectric material, plural device-forming regions each having an electrode, which are defined on opposite two surfaces of the thin plate. Each of the device-forming regions is isolated from an adjacent device-forming region by a stock-removal portion. Then, an electrically conductive layer is formed on the entire surface of one of the opposite two surfaces of the device substrate, and the device substrate is held on a stage through the conductive layer. On the other hand, a circuit pattern is formed on the other surface of the device substrate to electrically connect the electrodes. Next, the conductive layer is electrically connected to the circuit pattern to obtain a laminate on the stage, and the laminate is grounded so that all of the device-forming regions on the device substrate are at the same potential. Next, the laminate is treated with the blast to remove the pyroelectric material of the stock-removal portion, while leaving a bridge portion extending between adjacent device-forming regions and having the circuit pattern thereon, to thereby obtain a device-chip aggregate, in which adjacent device chips are coupled through the bridge portion. Subsequently, the device chip is separated from the device-chip aggregate by removing the bridge portion.
According to this method, it is possible to prevent the breakage of the polarization state of the pyroelectric material by static electricity developed during the blast treatment, and obtain the device-chip aggregate that facilitates the separation/collection of the device chips.
Further characteristics and effects brought thereby of the present invention will be understood in detail from the best mode for carrying out the invention described below, referring to the attached drawings.